Engine systems for vehicles and the like may comprise an aftertreatment module for removing unwanted gaseous emissions or pollutants from the exhaust gases of an internal combustion engine. In particular, a selective catalytic reduction system (SCR) may be provided in the exhaust gas system for removing nitrogen oxides (NOx). Typically, an SCR system comprises a reductant injector reaching into a mixing pipe located upstream of a catalyst. The reductant injector may inject a liquid reductant into the exhaust gases before they contact the catalyst. Suitable liquid reductants may include anhydrous ammonia, aqueous ammonia and urea. The high temperature of the exhaust gases may evaporate the liquid reductant and upon contact with the catalyst, the gaseous reductant may react with the NOx in the exhaust gas to form nitrogen and water.
However, if the exhaust gas temperature is too low, such as during low engine load conditions and in low duty cycles, the reductant may be deposited as solid compounds on components of the SCR system. In particular, the reductant may be deposited on or around an outlet nozzle of the reductant injector when eddy currents in the exhaust gas flow redirect injected reductant back onto the outlet nozzle. In addition, the reductant injector may undesirably leak small volumes of reductant, particularly when it is fully pressurized, onto the outlet nozzle. Since the outlet nozzle of the reductant injector may have a relatively low surface temperature due to low exhaust gas temperature, the redirected and leaked reductant may condense on it and the liquid components of the reductant may evaporate. Solid reductant deposits may subsequently be left on the outlet nozzle, which may therefore become partially or fully blocked. This may lead to increased reductant deposit growth and cause poor SCR system conversion efficiency. Additionally, for example, re-circulation zones in the exhaust mass flow caused by the design of the exhaust lines may cause deposits at or near a nozzle outlet of the reductant injector.
For example, US 2016/0298515 A1 of Perkins Engines Company Limited discloses a method of controlling an engine system having an aftertreatment module within which a reductant injector is located. The reductant injector may be controlled to inject reductant fluid to expel solid reductant deposits formed on the reductant injector.
The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.